A growing body of evidence demonstrates that younger age of onset for ASD treatment improves outcomes. Universal toddler screening for autism spectrum disorder (ASD) has been shown to lower the age of ASD diagnosis by two years compared to the national median; this in turn lowers the age of access to ASD-specific treatment. Yet on February 17, 2016, the US Preventive Services Task Force (USPSTF) published a final statement on autism screening in JAMA, in which they found insufficient evidence to recommend universal ASD screening. One of the primary gaps they identified was a lack of randomized controlled trials (RCTs) in which children detected through screening received treatment for ASD, with their outcomes compared to those of children not screened. The current proposal aims to fill this gap, connecting the dots between the screening and treatment literatures, and demonstrating that standardized, high-fidelity, universal screening lowers the age of diagnosis and treatment onset, leading to improved short- and long-term outcomes. The intervention in this RCT is supported deployment of such screening, with immediate evaluation of at-risk children, compared to a control group receiving usual care approaches to early detection of ASD, namely physician surveillance and/or unstandardized screening. In a sample of 8,000 toddlers enrolled through participating pediatric practices near Drexel University, the University of Connecticut, and the University of California Davis MIND Institute, we expect that cognitive functioning and ASD symptom severity will show greater improvements in the experimental group, in which most children will be detected at 18 m screening, compared to the control group, in which children are expected to be detected significantly later. In both groups, missed ASD cases will be detected through screening at 48 m. Across both groups, all children identified as at risk for ASD will receive a diagnostic evaluation, and all children diagnosed with ASD will be enrolled in one year of manualized early intensive behavioral treatment (EIBI). In addition to the primary outcome measures of cognition and symptom severity, exploratory outcomes will include group differences in adaptive functioning, kindergarten readiness, and social reciprocity as measured by experimental eye tracking and parent-child interaction ratings. We also will examine the impact of the screening intervention on physician attitudes and on parent empowerment and stress. Finally, we will examine potential moderators of group differences, to determine whether initial symptom severity, cognitive ability, or SES affects the expected superior response to treatment in the experimental group. Our Autism Centers of Excellence Network is uniquely positioned to carry out this study; our prior work demonstrates our extensive experience and productivity in the field of early screening and treatment in ASD. This study will be the first RCT of toddler ASD screening, and will use rigorous methods that have provided evidence for universal screening protocols in other medical fields. This study will have a significant impact on science, policy, and practice. By demonstrating that universal early screening leads to earlier treatment and better outcomes, this project will provide evidence for the benefits of universal ASD screening, including better social and cognitive functioning, mitigating lifespan disability, reducing societal costs, and improving personal well-being and productivity of individuals with ASD.